Electrodeposition of copper



latented Jan. 24, 1950 SATES PATENT OFFICE Ohio, assignors to The Harshaw Chemical Company, Elyria, Ohio, a corporation of Ohio No Drawing. Application December 21, 1946, Serial No. 717,800

Claims. I

This invention relates to electrodeposition of copper and more particularly to improved processes and solutions for electrodeposition of bright copper.

We have now discovered that excellent bright copper deposits can be made by the inclusion in the copper cyanide plating solution of a suitable quantity of an organic compound of the class consisting of:

B-mercapto ethanol (HOCI-IzCHzSI-I) Di thio diglycol (HOCI-IzCI-IzSSCHzCHzOH) B,B dihydroxyethyl sulfide (HOCH26H2SCH2CH2OH) Thioglycollic acid (HOCOCI-IzSI-I) That is, when such a deposit is made, it can be built up to substantial thickness, three ten-thousandths of an inch and more, and still exhibit greatly improved lustre as compared with the usual cyanide copper bath. Agitation of the solution results in improvement in lustre and makes possible the use of much higher current density, e. g. increase from a. s. f. to 60 a. s. f. Interruption of the current at intervals, e. g. 1 minute on, 10 seconds off, reversal of the current every few seconds or use of alternating current superimposed on the direct current, all tend to produce improved lustre and more uniform deposits.

The compound to be suitable should have adequate solubility in the copper cyanide bath to make possible the maintenance in solution of a sufiici'ent quantity of the addition agent to achieve the desired result. The concentration of addition agent required for best results varies among the above indicated addition agents. In the case of B-mercapto ethanol the concentration should not be less than 0.05 gram per liter nor more than 10 grams per liter, a preferred range being from about 1 to 4 grams per liter. In the case of dithio diglycol, the concentration should not be less than 0.04 gram per liter nor more than 1.8 grams per liter, the optimum being from about 0.6 to 1.0 gram per liter. In the case of thicglycollic acid, the concentrations may be rather low, not less than about 0.007 gram per liter but may also be as high as 35 grams per liter, a, preferred range being from 0.25 to grams per liter. In the case of 3,18 dihydroxyethyl sulfide the concentration may run from 1 gram per liter to as high as 240 grams per liter, a preferred range being from 4 to 70 grams per liter.

An aqueous alkaline plating bath may be employed containing 4 to ounces to 150 grams per liter) of CuCN per gallon and the requisite amount of NaCN. The preferred pH range is 9.5 to 11.5 but good results may be had from 8.5 to 12.5. Free cyanide content may be from 0 to 11.5 grams per liter or more, the preferred range being 2 to 12 grams per liter. In general, increase of free cyanide is desirable with increasing CuCN content. The temperature is preferably maintained between 130 F. and 150 F. although good results can be had between 120 F. and 160 F.

Current is passed through the above indicated solutions from a copper anode to acathode at a cathode current density of from a very low value up to amperes per square foot.

Preferred solutions and plating conditions would be, for example:

Example I CuCN grams per liter 30 Free cyanide do 12 B-mercapto ethanol do 4 Water Remainder pH 8.5 CD (continuous current) a. s. f 30 Temperature F 140 Example II CuCN "grams per liter" Free cyanide do 5 Dithiodiglycol do 0.6 Water Remainder pI-I 12.5 CD (continuous current) a. s. f 20 Temperature F Example III CuCN grams per liter 120 Free cyanide do 12 BB dlhydroxyethyl sulfide do 70 Water Remainder pH 12.5 C. D. (interrupted current, 30 sec. on; 10 sec.

Off a. s. f 15 This bath gave brighter deposits with interrupted current than with continuous current.

Example IV CuCN grams per Men. 30 Free cyanide do 2 Thioglycollic acid do 20 Water Remainder pH 10.0 CD (continuous current) a. s. f 20 Temperature ..F 140 Having thus described our invention, what we claim is:

1. An aqueous, alkaline electroplating bath which comprises an aqueous medium to which has been added a metal ion yielding material essentially consisting of copper cyanide in concentration from 30 to 150 grams per liter, a sufficient amount of sodium cyanide to produce from 2 to 12 grams per liter of free cyanide in the solution and an amount of a brightening addition agent of the class consisting of B-mercapto ethanol, dithiodiglycol, B,B dihydroxyethyl sulfide and thioglycollic acid sufiicient to permit a brilliant cathodic deposit of copper upon the passage of an electric current from a copper anode to a cathode through the bath, the concentration of said brightening addition agent being from 0.05 gram per liter to grams per liter in the case of B-mercapto ethanol, from 0.04 gram per liter to 1.8 grams per liter in the case of dithiodiglycol, from 0.007 gram per liter to 35 grams per liter in the case of thioglycollic acid, and from 1 gram per liter to 240 grams per liter in the case of B,B dihydroxyethyl sulfide.

2. A method which comprises electrodepositing copper from an aqueous, alkaline copper cyanide solution containing from 30 to 150 grams per liter of copper cyanide and from 2 to 12 grams per liter of free cyanide, there being added to such solution as a brightening agent a substance of the class consisting of B-mercapto ethanol, dithiodiglycol, B,B' dihydroxyethyl sulfide and thioglycollic acid, the concentration of said brightening addition agent being from 0.05 gram per liter to 10 grams per liter in the case of B-mercapto ethanol, from 0.04 gram per liter to 1.8 grams per liter in the case of dithiodiglycol, from 0.007 gram per liter to 35 grams per liter in the case of thioglycollic acid, and from 1 gram per liter to 240 grams per liter in the case of B,B' dihydroxyethyl sulfide.

3. An aqueous, alkaline electroplating bath which comprises an aqueous medium to which has been added a metal ion yielding material essentially consisting of copper cyanide in concentration from 30 to grams per liter, 2. sufficient amount of sodium cyanide to produce from 2 to 12 grams per liter of free cyanide in the solution and containing as an organic brightening addition agent B-mercapto ethanol in concentration from 0.05 to 10 grams per liter.

4. An aqueous, alkaline electroplating bath which comprises an aqueous medium to which has been added a metal ion yielding material essentially consisting of copper cyanide in concentration from 30 to 150 grams per liter, a sufficient amount of sodium cyanide to produce from 2 to 12 grams per liter of free cyanide in the solution and containing as an organic brightening addition agent 3,13 dihydroxyethyl sulfide in concentration from 1 to 240 grams per liter.

5. An aqueous, alkaline electroplating bath which comprises an aqueous medium to which has been added a metal ion yielding material essentially consisting of copper cyanide in concentration from 30 to 150 grams per liter, a sufficient amount of sodium cyanide to produce from 2 to 12 grams per liter of free cyanide in the solu tion and containing as an organic brightening addition agent dithiodiglycol in concentration from 0.04 to 1.8 grams per liter.

KARL S. VIILLSON. DAVID G. ELLIS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,147,415 Tucker Feb. 14, 1939 2,195,409 Flett July 29, 1940 2,402,640 Lazier et al June 25, 1945 2,410,844 Signaigo et al Nov. 12, 1946 2,424,887 Henricks Apr. 2, 1947 OTHER REFERENCES The Metal Industry, March 1943, pages 134- 137, and Apr. 1, 1943, page 206. 

1. AN AQUEOUS, ALKALINE ELECTROPLATING BATH WHICH COMPRISES AN AQUEOUS MEDIUM TO WHICH HAS BEEN ADDED A METAL ION YIELDING MATERIAL ESSENTIALLY CONSISTING OF COPPER CYANIDE IN CONCENTRATION FROM 30 TO 150 GRAMS PER LITER, A SUFFICIENT AMOUNT OF SODIUM CYANIDE TO PRODUCE FROM 2 TO 12 GRAMS PER LITER OF FREE CYANIDE IN THE SOLUTION AND AN AMOUNT OF A BRIGHTENING ADDITION AGENT OF THE CLASS CONSISTING OF B-MERCAPTO ETHANOL, DITHIODIGLYCOL, B,B'' DIHYDROXYETHYL SULFIDE AND THIOGLYCOLLIC ACID SUFFICIENT TO PERMIT A BRILLIANT CATHODIC DEPOSIT OF COPPER UPON THE PASSAGE OF AN ELECTRIC CURRENT FROM A COPPER ANODE TO A CATHODE THROUGH THE BATH, THE CONCENTRATION OF SAID BRIGHTENING ADDITION AGENT BEING FROM 0.05 GRAM PER LITER TO 10 GRAMS PER LITER IN THE CASE OF B-MERCAPTO ETHANOL, FROM 0.04 GRAM PER LITER TO 1.8 GRAMS PER LITER IN THE CASE OF DITHIODIGLYCOL, FROM 0.007 GRAM PER LITER TO 35 GRAMS PER LITER IN THE CASE OF THIOGLYCOLLIC ACID, AND FROM 1 GRAM PER LITER TO 240 GRAMS PER LITER IN THE CASE OF B,B'' DIHYDROXYETHYL SULFIDE. 